Variable electrical resistance and potentiometer



April 20, 1954 p, ox 2,676,227

VARIABLE ELECTRICAL RESISTANCE AND POTENTIOMETER Filed April 25, 1952 Patented Apr. 20, 1954 VARIABLE ELECTRICAL RESISTANCE AND POTENTIOMETER Paul Xavier Fox, .Horsforth, near Leeds, England Application April 25, 1952, Serial No. 284,465

6 Claims.

This invention relates to means for making a low torque resilient contact with an element, more particularly with the winding of a variable electrical resistance or potentiometer and has for its chief object to provide an improved form of contact assembly which will have the maximum flexibility with rigidity and a large amount of take up with a virtually constant pressure, the contact assembly being thus particularly applicable to fine wire potentiometers in which the rubbing contact has a light torque and pressure.

According to the present invention, the contact element is carried by a torsion bar or the like and is pressed into contact with the winding by the stress in said torsion bar or the like.

Preferably the contact arm extends out at right angles to the torsion bar or the like and is so constructed that there is little, if any, give in the arm itself.

Conveniently the member which is moved to adjust the contact is provided with two arms between the ends of which are mounted a plurality of strands of wire, the strands being twisted together at both ends to form the torsion bar, and at least one strand being extended out in triangular form at or near the centre to constitute the contact arm, the end of said contact arm being bent over, and the tip of the bent-over portion forming the contact proper.

In order that this invention may be more clearly understood and readily carried into effect, reference may be made to the accompanying drawings, which illustrate certain embodiments of the present invention as applied to the contact assembly of a variable electrical resistance or potentiometer, and in which:

Figure 1 is a perspective view of a variable electrical resistance provided with one form of contact according to the present invention, and

Figure 2 is a perspective view of the contact element itself on a somewhat larger scale,

Figure 3 is a section through part of a variable electrical resistance or potentiometer provided with a modified form of contact according to the present invention, and

Figure 4 is a perspective view of the contact element shown in Figure 3 on a somewhat larger scale.

Figure 5 is a perspective view of another modified form of contact according to the present invention,

Figure 6 is a perspective view of a further modified form of contact device according to the present invention and Figure 7 illustrates yet a further modification.

shown) Referring now more particularly to Figures 1 and 2 of the drawings, 10 is. the resistance element, and 1 I is a member adapted to be rotated. or moved by the adjusting knob or the like (not Outstanding from the rotatable mem her I l are two arms l2 between the ends of which are stretched two strands of wire. The strands of wire are twisted together at both ends, as at H, and the ends are soldered or otherwise secured to the arms l2. At or near the centre one strand is extended out in. triangular form as at M to constitute the contact arm. The end of the triangular portion !4 is bent over as at [5 and the tip of the same forms the contact proper, engaging with the resistance element Hi. In use, the contact assembly is so arranged that when the tip i5 is in contact with the winding $0, the twisted ends l3 of the strands are stressed to press the contact [5 into contact with the windingwith the desired degree of pressure.

The modification shown .in Figures 3 and 4 of the accompanying drawings is a double element contact which acts as a bridge, bridging the winding it and a collector ring 15. In this case three strands of wire are twisted together at their "ends as at i! and are secured to the arms- 12 as in the construction illustrated in Figures 1 and 2. One strand of wire at or near the centre is extended out in triangular form as at M, the end being turned down as at [5 to contact with the winding I0. One of the other strands is extended out in triangular form as at [8 and is bent so that its tip contacts with the collector ring 6. In this way both of the triangular parts tend to unwind under pressure and the desired low torque resilient contact is obtained both on the winding and also on the collector ring.

In the modified form of contact shown in Figure 5, only a single strand of wire 19 is stretched across the ends of the two arms l2, the centre portion being extended out in the form of a triangle 20 and the base parts of the triangle are clamped or soldered to a strip of metal or the like 2| extending across the base of the triangular form. The tip of the triangular portion. 20 is turned down as at 22 as previously described. In this construction, the two ends of wire act as torsion bars and the desired rigidity is secured in the contact arm which, it will be seen, extends out at right angles from the torsion elements.

In the further modified form of the present invention shown in Figure 6, the torsion bar element is in the form of alight strip 23, the contact arm 24 extending out at right angles thereto and being, if desired, ribbed or otherwise reinforced as at 25. In this embodiment, the torsion bar and contact arm assembly may be stamped out of metal strip as a single piece.

Yet a further modification of the present invention is illustrated in Figure 7 of the accompanying drawings where a light strip 26 is secured across the ends of the arms 12, the contact arm being in the form of a shaped wire 2'! the ends of which are soldered through the strip. In this case, as indeed in all constructions of contact assembly according to the present in vention, the rigidity of the contact arm exceeds that of the torsion bar so that the pressure of the contact with the element with which it engages is due to stress in the torsion bar as distinct from deflection of the contact arm itself.

The contact assembly according to the present invention is simple and cheap to produce has a maximum flexibility with rigidity and a large take-up with virtually constant pressure. It may easily be adjusted to give the desired degree of pressure on the winding by adjusting the torsion.

Although the present invention has been described herein as applied to the contacts of variable electrical resistances and potentiometers, and indeed it is particularly applicable to this purpose, it will be appreciated that the tion is not limited to this application, but is of general application where it is desired to obtain a low torque resilient contact with an element or elements. As examples of further pplications of the present invention may be mentioned a low torque contact for a commutator, a slip ring, a

stud switch or a sensitive relay contact, and it may also be applied as a light weight pen carrier for delicate pen recording instruments.

I claim:

1. Means for making a low torque resilient contact with an element, more particularly the winding of a variable electrical resistance, com-- prising a pair of spaced arms, a torsion bar element secured across said arms, and a triangular length or" wire having a bent-over end secured to said torsion bar element intermediate its the tip of said bent-over portion engaging with said element to make contact therewith, the arrangement being such that with said tip in engagement with said element the torsion bar element is stressed to maintain a low torque resilient contact between said tip and said element.

2. Means for making a low torque resilient tact with an element, more particularly the winding of a variable electrical resistance, corn prising a pair of spaced arms, a plurality of strands of wire twisted together at their ends in the same direction so as to form a torsion secured across said arms, at least one of said strands of wire being extended out in triangular 4 form intermediate its ends to engage at its tip with said element, the arrangement being such that with said tip in engagement with said element the torsion bar element is stressed to maintain a low torque resilient contact between said tip and said element.

3. Means for making a low torque resilient contact with an element, more particularly the winding of a variable electrical resistance, comprising a pair of spaced arms, a plurality of strands of wire twisted together at their ends in the same direction so as to form a torsion bar secured across said arms, at least one of said strands of wire being extended out in triangular form intermediate its ends and turned over so as to engage with its tip with said element, the arrangement being such that with said tip in engagement with said element the torsion bar element is stressed to maintain a low torque resilient contact between said tip and said element.

4. In means for making a low torque resilient contact with an element as claimed in claim, 3, means for adjusting said spaced arms relative to said element to give an adjustable contact.

5. Means for making low torque resilient contacts with two elements comprising a member capable of being moved to adjust the contacts, a pair of spaced arms carried by said member, at least three strands of Wire twisted togei or at their ends in the same direction so as to form a torsion bar secured across said arms, two of said strands being extended out into triangular forms intermediate their ends and turned over so as to engage with their tips the said two elements, the arrangement being such that with said tips in engagement with said elements, the single torsion bar is stressed to maintain independent low torque resilient contacts between said tips and said elements.

6. Means for making a low torque resilient contact with the Winding of a variable elec" 'ical resistance comprising a member capable of be 1g moved to adjust the contact, a pair of arms ried by said member, a torsion bar element secured across said arms and a contact element outstanding from said torsion bar element in engagement with the resistance element of the variable electrical resistance, the arrangement being such that with said contact in engagement with said resistance element the torsion bar is stressed to maintain a constant low torque resilient contact between said contact and said resistance element.

Name Date Rich May 31, 1949 Number 

